The subject invention generally relates to a variable displacement fluid translating device and more particularly to a digitally controlled variable displacement fluid translating device that is capable of controlling flow in both directions.
Variable displacement fluid translating devices are well known in the art and may be in the form of a fluid pump or a fluid motor. The displacement of these known types have typically been controlled by changing the angle of a cam plate, changing an eccentric of a rotating cam or by changing the timing of the inlet and outlet ports therein. The displacement of many of these known pump/motors are capable of operation in an overcenter position. That is, the flow direction with in the pump/motor is changed by the displacement mechanism being moved both directions from a zero displacement position. It is also known to change the displacement of a pump/motor by causing the flow from selected ones of the internal pistons to be bypassed across a solenoid controlled poppet valve to the low pressure side thereof. An example of such a variable displacement pump/motor is set forth in U.S. Pat. No. 5,259,738 issued on Nov. 9, 1993 to the University of Edinburgh. However, the pump/motor arrangement of U.S. Pat. No. 5,259,738 is only capable of operation in a two quadrant mode. It would be beneficial to have a fluid translating device in which the displacement thereof could be changed by controlling the fluid in and out of each individual piston therein and also be operational in a four quadrant mode.
The subject invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention, a fluid translating device is provided and comprises a housing, a rotating cam, a plurality of piston bores, a plurality of pistons, a plurality of pressure chambers and a valving arrangement. The housing has first and second inlet/outlet ports and defines a reference axis therethrough. The rotating cam is disposed in the housing along the reference axis and has a cam surface. The plurality of piston bores are defined in the housing about the reference axis and each bore of the plurality of piston bores has a bottom portion. The plurality of pistons are slideably disposed in the plurality of piston bores and are selectively in mating contact with the cam surface of the rotating cam. The plurality of pressure chambers are defined in the housing between the respective one of the plurality of pistons and the bottom portion of the respective ones of the plurality of piston bores. The valving arrangement is connected between selected pressure chambers of the plurality of pressure chambers and the respective first and second inlet/outlet ports. The valving arrangement is operative to selectively control the displacement and the direction of fluid flow in each pressure chamber relative to the first and second inlet/outlet ports.
In another aspect of the present invention, a method of controlling the displacement and the flow direction of fluid within a variable displacement fluid translating device between first and second inlet/outlet ports. The method comprises the following steps: provide a housing having first and second inlet/outlet ports and a reference axis; provide a rotating cam having a cam surface in the housing along the reference axis; form a plurality of piston bores in the housing about the reference axis; provide a plurality of pistons in the plurality of piston bores that are slideably disposed in the respective piston bores and that are selectively in mating contact with the cam surface of the rotating cam; establish a plurality of pressure chambers between the respective one of the plurality of pistons and the respective ones of the plurality of piston bores; and provide a valving arrangement between selected pressure chamber of the plurality of pressure chambers and the respective first and second inlet/outlet ports. In the method each valving arrangement is operative to selectively control displacement and the flow direction in each pressure chamber relative to both of the first and second inlet/outlet ports.